Telemarketers use dialers and computers to dial out. Most are spoofed numbers.
Report them here:

https://www.ftccomplaintassistant.gov/#&panel1-1
https://esupport.fcc.gov/ccmsforms/form1088.action
https://complaints.donotcall.gov/complaint/complaintcheck.aspx?panel=2
http://www.consumerfinance.gov/complaint/
http://www.stopfraud.gov/report.html